1. Field of the Invention
The present invention relates to a projector type vehicular headlamp and more particularly to a vehicular headlamp that has therein a moveable shade.
2. Description of the Related Art
Generally, a projector type headlamp includes a projection lens disposed on an optical axis extending in a longitudinal direction of the vehicle, a light source disposed to the rear side of a rear side focal point of the projection lens, and a reflector that reflects light from the light source toward the optical axis. When the projector type headlamp generates a low beam light distribution pattern, a shade provided so that its upper end edge is in the vicinity of the optical axis near the rear side focal point of the projection lens shields a part of the reflected light from the reflector, thus forming a predetermined cut-off line at the upper edge of the low beam light distribution pattern.
Japanese Patent Application Laid-Open (Kokai) No. 2003-257218 discloses a projector type vehicle headlamp, and this headlamp includes a movable shade that can be moved between a light shielding position, where the upper end edge of the moveable shade is positioned in the vicinity of the optical axis near the rear side focal point, and a light transmitting position, at which, as compared to the light shielding position, the amount of reflected light from the reflector that is shielded is reduced.
In the vehicular headlamp of Japanese Patent Application Laid-Open (Kokai) No. 2003-257218, the movable shade is moved to the light transmitting position in order to generate a high beam light distribution pattern. Thus, a single lamp is used for both the low beam and the high beam. Moreover, the upper end edge of the movable shade is curved to extend substantially along the rear side focal plane of the projection lens when the movable shade is in the light shielding position. As a result of this configuration, the cut-off line of the low beam distribution pattern appears distinctly.
The moveable shade of the above-described related art is rotatable about a rotational axis line that extends in the width direction of the vehicle, and this rotational axis line is located at the lower end of the moveable shade and is at a position that is fairly distance from the center of gravity of the moveable shade. As a result, the upper end edge of the moveable shade tends to wobble due to the vibrations of the vehicle, etc., and thus the position of the cut-off line of the low beam distribution pattern tends to change.
In order to suppress this type of wobbling movement, the above-described vehicular lamp has a built-in return spring in the actuator that rotates the moveable shade. The movable shade is normally elastically urged toward the light shielding position by a return spring.
However, in order to effectively suppress the occurrence of this wobbling movement, it is necessary to set the spring constant of the return spring to a somewhat large value. As a result, the driving force required from the actuator for rotating the moveable shade also has to be somewhat large. This in turn makes it difficult to reduce the size and weight of the actuator and to reduce the cost.
Difficulties similar to the above occur not only when switching from the low beam distribution pattern to the high beam distribution pattern but also when switching from the low beam distribution pattern to an intermediate distribution pattern (which is an intermediate distribution pattern that is between the low beam distribution pattern and the high beam distribution pattern).